In a conventional HDCP architecture, a single protected port of a receiving device requires a dedicated pipe and an HDCP engine. A receiving device with n ports, therefore, requires n pipes and n HDCP engines. An improvement over the conventional HDCP architecture allows multiple ports to be supported by only two pipes, a main pipe and a time-based roving pipe.
One problem of the improved architecture is that a port may lose a first CTL3 (encrypt synchronization signal) signal from a transmitting device if no pipe is selected for the port when the first CTL3 comes in. Some devices may detect such a situation using a method of Ri comparison. Many transmitting devices on the market, however, cannot detect Ri mismatches and perform a re-authentication to fix the problem. In such a case, the user will see snow noise on the display device rather than the desired viewing data. If the input stream is an HDMI stream, this issue may be resolved using ECC error. However, for a DVI stream, since there is no audio packet, there is no ECC error even if there is a Ri mismatch; hence, snow noise may continue indefinitely.
It is therefore desirable to be able to detect a situation at the receiving device where a port in a time-based roving architecture has lost a CTL3 signal from a transmitting device.